Coaxial cable antenna coupler



Oct. 23, 1962 J. P. DOLAN 3,060,428

COAXIAL CABLE ANTENNA COUPLER Filed Feb. s. 19Go JAMES P. DCLAN FIG-...6 INVENTOA United States Patent O 3,060,428 COAXIAL CABLE ANTENNA COUPLER James P. Dolan, 8214 42nd Ave. NE., Seattle, Wash. Filed Feb. 8, 1960, Ser. N0. 7,329 Claims. (Cl. 343-851) This invention relates to an antenna coupler and, more particularly, to an elongated, shielded, conductive connector to be used between a radio transmitter and the associated antenna on land, sea and space vehicles.

The primary object of this invention is to provide improved functioning of short wave radio transmitters under circumstances Where satisfactory grounding or earthing is diicult to attain. Another object lies in the provision of a coupler between a radio transmitter and its antenna which is simply produced, inexpensive, easy to install and use, and which improves radio transmission under conditions where grounding is obtained only with diiculty or with undesirable accompanying side effects, and with improvement in the quality of transmission even with conventional grounding apparatus presently used.

In the following description of the invention and in the accompanying drawings is disclosed a preferred form of apparatus according to this invention. Also, an alternative form of the invention is disclosed. Variations and modiiications of these forms will occur to those skilled in the art and all such that are the equivalent of the invention herein disclosed and that fall within the spirit andv scope of the subjoined claims are to be considered a part of this invention.

In the drawings:

FIG. l is a diagrammatic perspective view of a transmitter coupled to an antenna;

FIG. 2 shows a coupler according to this invention, portions having been broken away or omitted for convenience of illustration;

FIGS. 3, 4 and 5 are cross-sections taken on lines 3 3, 4-4 and 5-5, respectively, of FIG. 2;

FIG. 6 shows-an alternate form of coupler.

Radio transmitter unit 10 is provided with connector posts or terminals A, for an antenna lead, and G for a ,groundl wire. Antenna 12 rises from coil 14 on antenna post 16 which may be supported upright by a mounting plate or base 18, normally attached to the vehicle in which the transmitter is installed.

A coupler, according to this invention, comprises an elongated conductor wire 20 which, by means of a connector lug 22, is attached to the antenna terminal or connector post A of transmitter 10. Conductor 20 extends from the transmitter and terminates without connection in close proximity to antenna mast 16.

A first shield section 24 coaxially surrounds a portion of conductor 20 near the transmitter unit 10. Preferably such a shield is formed of a plurality of Wires woven or braided into cylindrical form about a tubular insulator sleeve 26 which encases or jackets conductor 20 from end to end. An insulated conductor 23 having lug 30 is connected with and extends from that end of shield portion 24 nearest the transmitter 10 for connection to terminal G as shown in FIG. l. Conductor 28 is otherwise unconnected in a conductive sense.

A second shield section 32 also coaxially surrounds another portion of conductor 20. Shield 32 is arranged in end to end spaced apart relation to section 24 as shown in FIG. 2. Shield section 32, likewise formed of woven or braided wires, surrounds .insulator 26 and is spaced thereby about conductor 20. That end of shield section 32 nearest to and spaced from the unconnected outer end of shield section 24 is also unconnected. However, the opposite or remote end of shield 32 is connected to 3,060,428 Patented Oct. 23, 1962 'ice conductor 34 having connector lug 36 thereon for attachment to antenna mast 16.

Preferably the coupler throughout its length is covered by a protective and insulative jacket or casing 38. Insulative caps 40 cover the connections between shields 24 and 32 and the conductors 2S and 34 respectively.

It has been found practical to construct a coupler according to this invention by using a shielded microphone-type coaxial cable known commercially as Belden 8401. In such a cable the axial conductor wire 20 is No. 25 AWG. The shield portion of such a cable from which is formed shields 24 and 32, is a cylinder of braided or woven strands of No. 33 tinned copper wire. The insulator sleeve 26 around conductor 20 and inside shields 24 and 32 is formed of polyethylene material. The jacket 3S is formed of a vinyl compound. Preferably, ends of the wires forming the ends of shields 24 and 32 are unlaid and gathered together to form pigtails in conventional manner and the same are soldered to conductors 28 and 34 respectively. The formation of the two shields 24 and 32 from a cable such as Belden 8401 is easily accomplished by stripping or opening a medial portion of jacket 38. Then, cutting away a portion of the shielding forms the separated but juxtaposed shield sections 24 and 32. It is desirable that a non-conductive jacket 42 be closely secured about the gap for insulative purposes.

Where the unit 10 is of the type rated as a 2 to 3 megacycle transmitter it is desirable that the length of shield 24 be approximately 54 inches long. Shield 32 in such case may be the same length or longer, its length determining the width of the broadcast band desired. Where the unit 10 is rated as 5.5 megacycle transmitter, shield 24 desirably should be about 20 inches in length. In general, the higher the band rating of the transmitter the shorter should be shield 24. Conversely, the lower the band rating of the transmitter the greater the length of shield 24. j It will be seen that the coupler essentially comprises the conductor 20 which is connected to and extends from the antenna connector terminal A into close proximity to the antenna mast 16 to which there is no direct connection of the conductor 20. The conductor is coaXially surrounded by a rst shield 24 and a second shield 32, the same being spaced from each other in end to end but vunconnected relation. An end ofthe irst shield 24 nearest the connected end of conductor 20 is connected to the grounding terminal G of the transmitter unit 10. An end of the second shield 32 nearest the unconnected end of conductor 20 is connected to the antenna mast 16. Suitable insulation 26 separates conductor 20 from the shield sections 24 and 32. The Awhole assembly, when installed, is suitably insulated as by jacket 38 from conductive contact with all extraneous metal or other conductive elements.

An alternative form of coupler, shown in FIG. 6, comprises conductor 50, first shield section 52, second shield 54, and interposed therebetween intermediate shield section 56. Shield 52 as above described is to be connected by lead S3 to the transmitter connector G. Conductor 55 extends between shield 54 and the antenna mast. Shield S6 is unconnected. The coupler of FIG. 6 is suitable for long runs between transmitter and the antenna. The conductor 50 on one end only is connected to terminal A of a transmitter unit 10. Jackets 58 insulate the gaps between shields 52 and 56 and between shields 56 and 54 as described above.

VHaving thus described the invention, what is claimed l. A radio transmission system comprising; a transmitter unit having a ground terminal and an antenna terminal, an antenna; and a coaxial coupling circuit extending between said transmitter unit and said antenna, said coupling circuit comprising; an elongated conductor extending from said antenna terminal to a point adjacent to one end of said antenna, and a first and second coaxial shield in spaced apart end-to-end relation to each other and surrounding portions of said conductor, thereby forming a first and second capacitor connected in series; said first shield connected to the ground terminal and said second shield connected to the antenna, said shields each having a length which is within the range of one fiftieth to one-hundredth of the average wave length of the radio power transmitted.

2. A radio transmission system comprising; a transmitter unit adapted to transmit radio frequency power and having a ground terminal and an antenna terminal; an antenna positioned at a distance from said unit; and a coaxial coupling circuit extending between said transmitter unit and said antenna; said coupling circuit comprising; an elongated conductor extending from said antenna terminal to a point adjacent to one end of said antenna, and a first and second coaxial shield in spaced apart end-to-end relation to each other and surrounding portions of said conductor, thereby forming a first and second capacitor connected in series; said first shield connected only to the ground terminal and said second shield connected only to the antenna, said shields each having a length which is within the range of one-liftieth to one-hundredth of the average wave length of the radio frequency power transmitted by the unit and antenna.

3. A radio transmission system comprising; a transmitter unit adapted to transmit radio frequency power and having a ground terminal and an antenna terminal; an antenna positioned at a distance from said unit; and a coaxial coupling circuit extending between said transmitter unit and said antenna; said coupling circuit cornprising; an elongated conductor extending from said antenna terminal to a point adjacent to one end of said antenna, and a first and second conductive coaxial shield in spaced apart end-to-end relation to each other and surrounding portions of said conductor, said shields being supported on said elongated conductor by solid dielectric insulation material, thereby forming a rst and second capacitor connected in series; said first shield connected only to the ground terminal and said second shield connected only to the antenna, said shields each having a length which is `within the range of one-fiftieth to onehundredth of the average wave length of the radio frequency power transmitted by the unit and antenna.

4. A radio transmission system comprising; a transmitter unit adapted to transmit radio frequency power and having a ground terminal and an antenna terminal, said terminals for connection to a utilization circuit using said power; an antenna positioned at a distance from said unit and including a portion containing a series connected inductor; and a coaxial coupling circuit extending between said transmitter unit and said antenna; said coupling circuit comprising; an elongated conductor extending from said antenna terminal to a point adjacent to one end of said antenna, and a first and second conductive coaxial shield in spaced apart end-to-end relation to each other and surrounding portions of said conductor, said shields being substantially equal in length, said shields being supported on said elongated conductor by solid dielectric insulation material, thereby forming a rst and second capacitor in series; said first shield connected only to the ground terminal and said second shield connected only to the antenna, said shields having a length which is within the range of one-fiftieth to onehundredth of the average wave length of the radio frequency power transmitted by the unit and the antenna.

5. A radio transmission system comprising; a transmitter unit having a ground terminal and an antenna terminal; an antenna; and a coaxial coupling circuit extending between said transmitter unit and said antenna; said coupling circuit comprising; an elongated conductor extending from said antenna terminal to a point adjacent to one end of said antenna, and three coaxial shields in spaced apart end-to-end relation and surrounding portions of said conductor thereby forming three capacitors each having one side connected to said conductor; said first shield connected only to the ground terminal, said second shield connected only to said antenna, said third shield interposed between the first and second shields without contact with either shield or conductor, said shields each having a length which is within the range of one-fiftieth to one-hundredth of the average wave length of the radio power transmitted.

References Cited in the le of this patent UNITED STATES PATENTS 1,744,091 Wrape Jan. 2l, 1930 2,521,550 Smith Sept. 5, 1950 2,569,687 Pan Oct. 2, 1951 2,606,964 Gluyas Aug. 12, 1952 2,628,312 Peterson et al. Feb. 10, 1953 FOREIGN PATENTS 478,343 Germany June 21, 1929 700,559 Germany Dec. 23, 1940 OTHER REFERENCES The A.R.R.L. Antenna Book, published by the American Radio Relay League, 1956 (page 114 relied on). 

